Large Teleseismic P Wavefront Deflections Observed with Broadband Arrays
Large Teleseismic P Wavefront Deflections Observed with Broadband Arrays
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用宽带阵列观测到的大型远震 P 波前偏转
DOI：
10.1785/0120020126
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发表时间：
2003
影响因子：
3
通讯作者：
J. Eakins
中科院分区：
文献类型：
--
作者：
V. Schulte‐Pelkum;F. Vernon;J. Eakins
我们在大口径（150 km）宽带阵列上测量了平面波前入射方位角。入射方位角是由垂直分量地震图上P波至的互相关确定的。所考虑的周期范围为10至35秒。在南加州的Anza阵列，平面波方向偏离事件的大圆方位角达20°。此外，我们发现了一个令人惊讶的强大的频率依赖性相同的幅度和一个引人注目的反对称模式的偏转作为一个功能的backazimuth，而波前的曲率是小的。在德国的Grafenberg台阵和挪威的NORSAR台阵也发现了类似的特征，但振幅要弱得多，为1.5 °。我们归因于在安扎的行为结构在下地壳和上地幔的阵列下，考虑到观测结果只是一个函数的源backazimuth，而不是源深度和源机制，所考虑的波长范围从50到270公里，和该偏差的符号是相反的预测从浅地壳结构和莫霍面地形。我们能够重现的波前偏转的幅度和频率的依赖性，通过简单的二维结构，使用有限差分数值模拟平面波传播。
We measure the plane wavefront incidence azimuth for teleseismic P at large-aperture (∼50 km) broadband arrays. The incidence azimuth is determined by crosscorrelation of the P arrivals on the vertical component seismograms filtered in successive frequency bands. The periods considered range from 10 to 35 sec. At the Anza array in southern California, the plane wave direction is deflected from the great circle azimuth of the event by up to 20°. In addition, we find a surprisingly strong frequency dependence of the same magnitude and a striking antisymmetric pattern of the deflection as a function of backazimuth, whereas the curvature of the wavefront is small. Similar characteristics are found at the Grafenberg array in Germany and the NORSAR array in Norway, however, with much weaker amplitudes of ∼5°. We ascribe the behavior at Anza to structure in the lower crust and uppermost mantle beneath the array, given that the observations are only a function of source backazimuth and not of source depth and source mechanism, that the wavelengths under consideration range from 50 to 270 km, and that the sign of the deviation is opposite to that predicted from shallow crustal structure and Moho topography. We are able to reproduce the magnitude and frequency dependence of the wavefront deflection using finite difference numerical modeling of plane wave propagation through simple 2D structures.